The purpose of this study is to evaluate the relationship between hair dye use and breast cancer. Several studies have suggested that use of hair dye may increase a woman's risk of developing breast cancer, although other studies have found no such effect. Since about 25 million women in the U.S. dye their hair, it is important to determine whether hair dyes play a role in the development of breast cancer. The present study attempts to settle this issue by comparing the amount of hair dye used by a group of women with breast cancer and a group without the disease. The carcinogenicity of hair dyes has been in question since a number of them were found to be mutagenic in a bacterial test system. The results of animal and human studies on this question have been conflicting. The present study focuses on the association between hair dye use and the development of breast cancer. The study participants consist of approximately 500 women in whom breast cancer was detected at a large breast cancer screening center in New York City and a control group of approximately 1000 randomly selected screenees without breast cancer. Patterns of previous hair dye use among the breast cancer cases and the controls will be ascertained through interview and compared statistically to determine whether the two groups differ significantly in their use of hair dyes.